Drinking flask



FIG. 1 is an isometric view of a drinking flask showing our new design;

FIG. 2 is front view thereof;

FIG. 3 is a left side view thereof;

FIG. 4 is a right side view thereof;

FIG. 5 is a top plan view thereof; and,

FIG. 6 is a bottom plan view thereof.

The broken lines in the drawings depict portions of the drinking flaskthat form no part of the claimed design.

CLAIM The ornamental design for a drinking flask, as shown anddescribed.